1. Field of the Invention
The present invention relates to a tire building drum which is employed in a tire building and shaping process, and more particularly to such drum used for carrying out building and shaping of a green tire while gripping its bead portions. This drum is also utilized at the time of carrying out an appearance inspection while supporting beads of a tire in a tire inspection process.
2. Description of the Prior Art
Normally, upon fabrication of a radial tire, a green tire is built through two separate processes, and in the first process, a cylindrical green case is made. In the second process, a pair of drums disposed on a same axis in such manner that they can approach to and separate from each other, are employed, the bead portions at the opposite ends of the above-mentioned green case are made to be held by bead holding sections provided on the outer circumferential portions of the respective drums, and the above-mentioned green case is inflated and deformed into a toroidal shape by feeding high-pressure fluid into the green case and also making the respective drums approach to each other, under the above-mentioned condition. Then, by sticking a tread rubber onto the outer circumferential surface of the green case deformed into a toroidal shape through the above-mentioned process, a green tire is built and shaped.
A forming drum used in the above-described second process in the aforementioned radial tire building method, is disclosed in U.S. Pat. No. 4,472,233.
This forming drum includes an outer ring member fitted around a rotary shaft via an inner ring member or via an inner ring member and an intermediate ring member. On the above-mentioned outer ring member are provided a large number of drum segments severed along the circumferential direction and capable of protruding and entering in the radial directions. The radially outer end portions of the drum segments form a bead holding section for gripping the bead portions of the green case, and at the inner end portions thereof are rotatably supported rollers serving as cam followers.
On the other hand, a ring-shaped cylinder chamber is formed to surround the outer circumferential surface of the above-mentioned outer ring member, and a ring-shaped piston is fitted in the above-mentioned cylinder so as to be freely slidable in the axial direction. At one end of the piston is formed a conical inclined surface serving as a cam surface. The above-mentioned inclined surface and the aforementioned roller are engaged with each other. Accordingly, when the piston slides in the axial direction, the above-described drum segments (the bead holding section) would protrude or enter in the radial directions (expand or contract). And, the drum segments forming the bead holding section and the piston, the cylinder chamber and the like forming the bead holding section expanding and contracting mechanism, are assembled integrally with the above-described outer ring member.
Although the amount of expansion and contraction of the drum segments can be adapted to a certain degree of variation of a bead inner diameter with respect to tires having a same rim diameter, in the case where a tire rim diameter is different, the amount of expansion and contraction cannot be adapted to the difference of the bead inner diameter. Accordingly, in the case where, an attempt is made to form a tire having a different rim diameter, that is, upon switching of a tire size, the entirety of the integrally assembled bead holding section, expanding/contracting mechanism and outer ring member must be replaced as one unit.
In such a heretofore known forming drum, since the weight of the unit to be replaced upon switching of a tire size is heavy, the replacing work would become very laborious work. Also, significant time is necessitated for the switching.
In addition, since the unit to be replaced becomes large-sized, the place for keeping the units necessitates a sufficient amount of mechanical strength.
Furthermore, because of the fact that for each rim diameter of a tire, the entire unit including not only the bead holding section but also the expanding/contracting mechanism and the ring members must be fabricated and prepared, production costs rise.
Moreover, it is difficult to automate dismounting and mounting of the unit to be replaced.